Mollweide Equal Area

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The second oldest pseudocylindrical projection that is still in use (after the Sinusoidal) was presented by Carl B. Mollweide (1774-1825) of Halle, Germany, in 1805. It is an equal-area projection of the Earth within an ellipse. It has had a profound effect on world map projections in the 20th century, especially as an inspiration for other important projections, such as Van der Grinten.

Construction

Pseudocylinder

Property

Equal-area

Meridians

All of the meridians are ellipses. Central meridian is a straight line, and 90° meridians are circular arcs (Pearson, 1990).

Parallels

Equator and parallels are straight lines perpendicular to central meridian, but they are not equally spaced.

Graticule spacing

Linear graticules include central meridian and Equator (Environmental Systems Research Institute, 1992). Meridians are equally spaced along the Equator and along all other parallels. Parallels are straight parallel lines, but they are not equally spaced. Poles are points.

Linear scale

Scale is true along latitudes 40°44’N and S. Distortion increases with distance from these lines and becomes severe at the edges of the projection (Environmental Systems Research Institute, 1992).

Uses

World maps (Pearson, 1990).

Thematic or distribution mapping of the entire world, frequently in interrupted form (Environmental Systems Research Institute, 1992).

Mollweide is normally used for world maps and occasionally for a very large region, such as Pacific Ocean. This is because only two points on Mollweide are completely free of distortion unless the projection is interrupted. These are the points at latitudes 40°44’12"N and S on central meridian or meridians.

The world is shown in an ellipse with the Equator, its major axis, twice as long as the central meridian, its minor axis. The meridians 90° east and west of the central meridian form a complete circle. All other meridians are elliptical arcs which, with their opposite numbers on the other side of the central meridian, form complete ellipses that meet at the poles.